The present invention relates to an improved apparatus and method for providing a more complete incineration of waste gases, including any oily and/or flammable particles thereof, such as from reaction processes, prior to the entry of the waste gas by-products into a duct system leading to scrubbers and/or direct discharge into the atmosphere.
Reference is made to my U.S. Pat. No. 4,661,056, issued Apr. 28, 1987, for its disclosure of an apparatus which is designed for the controlled incineration of waste gases and which functions by introducing the combustible waste gases under low pressure to an air conduit, through a controlled combustion conduit in which the waste gases are mixed with swirling air, ignited and then drawn into the air conduit and conveyed through a scrubber at the exit end of the air conduit for release as non-combustible reaction products.
Controlled combustion devices and purging devices for combustible waste gases must be capable of operation under low pressures since such waste gases commonly are by-products of reactions which take place at or slightly above atmospheric pressure and which require the laminar flow of combustible reaction gases or by-product gases through the reactor. Any attempt to increase the pressure of the waste gases as they enter the controlled combustion conduit can lead to back-pressure problems within the reactor. However, the exposure of the combustible waste gases at relatively low pressures, i.e., atmospheric or only slightly higher, and a malfunction which allows air or some other oxidizing material to mix with the waste gas to the ignition means in a combustion chamber, in the case of controlled combustion devices, or to an unintentional spark or other accidental ignition source within the transport conduit or scrubber, in the case of non-incineration purging systems, creates the danger that the controlled fire within the combustion conduit or accidental fire within the conduit might flash back upstream through the reactor exhaust pipe into the reactor or other processing equipment creating disruptive and possibly dangerous conditions. The flame propagation rate of hydrogen and air, for example, is about 8.25 feet per second, which permits the flame to travel upstream against the low pressure flow of a waste gas containing hydrogen.
The apparatus of my aforementioned Patent is an incineration apparatus which assists the mixing of air with the waste gas by creating a swirling action and vacuum within the air conduit, at the downstream end of the waste gas conduit, beyond a combustion chamber.
While it is known to use a variety of commercially-available flame-arresting devices in waste gas processing systems to prevent or reduce the dangers discussed above, such devices are only effective against the flashing of the flame back upstream from the ignition chamber. However, if the incineration of the waste gases is incomplete such as those found in the exhaust from elastomer coating or curing ovens or those emitted by roughing pumps connected to the equipment for the plasma deposition of silicon nitride films, i.e., silane, ammonia, nitrogen, argon and oil vapor, such gases and/or oil vapors or other combustible materials pose a downstream danger of uncontrolled fire which can be swept through the duct system by the downstream movement of air. For example, flammable oily components of the waste gases can deposit on the inner walls of the duct as a layer which builds up over a period of time and entraps other combustible materials. If a condition arises which ignites the flammable oils and/or other combustible materials an uncontrolled fire can result, which fire can propagate and be swept through the duct system. An example of this condition can be illustrated with an analysis of deposits found in the ductwork of one such system. The solids were composed of 99.48% volatile components which were flammable and unpredictably pyrophoric.
It is the principal objective of the present invention to provide a new and improved apparatus and method for the complete incineration of waste gases, including oil vapors and other combustible materials present therein, so as to prevent the possibility of ignition thereof, downstream of the incinerator, resulting in uncontrolled fire within the duct system leading to scrubbers and/or the safe discharge to the atmosphere.